Subversion Repositories openrisc_2011-10-31

/* @(#)s_ilogb.c 5.1 93/09/24 */

/*

 * ====================================================

 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.

 *

 * Developed at SunPro, a Sun Microsystems, Inc. business.

 * Permission to use, copy, modify, and distribute this

 * software is freely granted, provided that this notice

 * is preserved.

 * ====================================================

 */

/*

FUNCTION

       <<ilogb>>, <<ilogbf>>---get exponent of floating-point number

INDEX

        ilogb

INDEX

        ilogbf

ANSI_SYNOPSIS

        #include <math.h>

        int ilogb(double <[val]>);

        int ilogbf(float <[val]>);

TRAD_SYNOPSIS

        #include <math.h>

        int ilogb(<[val]>)

        double <[val]>;

        int ilogbf(<[val]>)

        float <[val]>;

DESCRIPTION

        All nonzero, normal numbers can be described as <[m]> *

        2**<[p]>.  <<ilogb>> and <<ilogbf>> examine the argument

        <[val]>, and return <[p]>.  The functions <<frexp>> and

        <<frexpf>> are similar to <<ilogb>> and <<ilogbf>>, but also

        return <[m]>.

RETURNS

<<ilogb>> and <<ilogbf>> return the power of two used to form the

floating-point argument.  If <[val]> is <<0>>, they return <<-

INT_MAX>> (<<INT_MAX>> is defined in limits.h).  If <[val]> is

infinite, or NaN, they return <<INT_MAX>>.

PORTABILITY

        Neither <<ilogb>> nor <<ilogbf>> is required by ANSI C or by

        the System V Interface Definition (Issue 2).  */

/* ilogb(double x)

 * return the binary exponent of non-zero x

 * ilogb(0) = 0x80000001

 * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)

 */

#include "fdlibm.h"

#include <limits.h>

#ifndef _DOUBLE_IS_32BITS

#ifdef __STDC__

        int ilogb(double x)

#else

        int ilogb(x)

        double x;

#endif

{

        __int32_t hx,lx,ix;

        EXTRACT_WORDS(hx,lx,x);

        hx &= 0x7fffffff;

        if(hx<0x00100000) {

            if((hx|lx)==0)

                return - INT_MAX;       /* ilogb(0) = 0x80000001 */

            else                        /* subnormal x */

                if(hx==0) {

                    for (ix = -1043; lx>0; lx<<=1) ix -=1;

                } else {

                    for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;

                }

            return ix;

        }

        else if (hx<0x7ff00000) return (hx>>20)-1023;

        else return INT_MAX;

}

#endif /* _DOUBLE_IS_32BITS */